Nitrogen oxides are formed when fossil fuels, such as oil, gas and coal, are burned at high temperatures in combustion engines of power plants, furnaces, off-road equipment, etc.
As is all too well understood in the art, nitrogen oxides so formed can cause acid rain, ozone depletion, photochemical smog and catastrophic greenhouse effects. Furthermore, these chemicals can be harmful to the growth of living creatures, such as special plant varieties. It is also known that small levels of NOx can cause nausea, irritated eyes and nose, fluid forming in the lungs and shortness of breath in mammals, including humans. Furthermore, reduced oxygen intake, swelling of the throat, a large buildup of fluids in the lungs, and even death can be caused by breathing in an atmosphere containing high levels of NOx. The curtailment of these substances generally in the atmosphere and particularly in work places is, therefore, of paramount interest.
The United States Environmental Protection Agency (EPA) has set forth stringent standards for NOx pollution on any type of NOx emission sources, such as motor vehicles and power plants.
The selective catalytic reduction of the nitrogen oxides by ammonia is known as the best process for the reduction of NOx in off-road equipment and stationary sources.
There is, therefore, a present need for improved catalytic reduction processes for the removal of NOx molecules, such as in the reduction of the requisite operating temperatures for an NOx reduction process.
There is also a present need to increase the NOx removal efficiency in selective catalyst reduction technologies.
The prior art includes various techniques with limited conversion efficiencies, i.e., well below 100%, and usually at high temperatures, e.g., 450° C., making these techniques of limited applicability to actually reduce noxious nitrogen oxide emissions. Copper and iron are sometimes used as a catalyst for NOx abatement, where a copper catalyst shows at about 90% conversion in a temperature range of about 250° C. to 450° C. Also, an Iron catalyst provided a similar conversion value at temperatures from 355° C. to 625° C.
One disadvantage in the use of these catalysts, however, relates to the over-oxidation of ammonia to nitrous oxide at temperatures above 670° C., which reduces the efficiency of the reduction and the practical usefulness of these prior art techniques.
It is, therefore, an object of the present invention to lower the operating temperature for the reduction to more manageable levels.
It is also an object of the present invention to increase the efficiency of the reduction to greater than or equal to 99% and nearly or at 100%.
Furthermore, it is an object of the present invention to increase the life of the catalysts, further increasing the efficiency of the process.
These objects are met in one embodiment of the present invention where there is a significant reduction in the operating temperature, which enables a 100% (complete) conversion at a temperature less than 80° C. As a result of this advancement in the technology, a selective catalytic reduction (SCR) unit may now be located far from the combustion chamber, where the gaseous byproducts have cooled. Moreover, such a lowered conversion/reduction reaction temperature avoids over-oxidation of ammonia and, hence, increases the catalyst lifetime, offering significant advantages over the known prior art.
Even in prior art techniques where the efficiency of the aforementioned catalyst is near 100%, Applicant has found that this achievement comes at significant cost, e.g., requiring a pre-oxidation unit to convert NO to NO2 prior to the SCR unit.
It is, accordingly, an object of the present invention to provide an improved nano-hybrid catalyst, enabling at or about 100% efficiency at low temperatures, without requiring a pre-oxidation unit.
It is a further object of the present invention that the technique of the claimed invention be a simple and straightforward preparation procedure, as well as providing high efficiencies, for the conversion of nitrogen oxides at low temperatures from about 50° C. to 200° C. by the use of a nano-hybrid catalyst made of carbon nanotubes and metal ferrite.
It is, therefore, an object of the present invention to provide improved catalysts for NOx reduction.